The phosphor is utilized in a fluorescent display tube (VFD: Vacuum-Fluorescent Display), a field emission display (FED: Field Emission Display or SED: Surface-Conduction Electron-Emitter Display), a plasma display panel (PDP: Plasma Display Panel), a cathode-ray tube (CRT: Cathode-Ray Tube), a liquid-crystal display backlight (Liquid-Crystal Display Backlight), a white light-emitting diode (LED: Light-Emitting Diode), and so on. In any of these applications, it is necessary to provide the phosphor with energy to excite the phosphor in order to make the phosphor emit fluorescence and the phosphor is excited by an excitation source with high energy such as a vacuum ultraviolet ray, an ultraviolet ray, an electron beam, and blue light so as to emit a visible light ray such as blue light, green light, yellow light, orange light, and red light. However, as a result of the phosphor being exposed to such excitation source, the luminance of the phosphor tends to decrease and a phosphor having little degradation in the brightness is desired. Therefore, a phosphor having an inorganic crystal containing nitrogen in a crystal structure thereof as a host crystal, instead a conventional phosphor such as a silicate phosphor, a phosphate phosphor, a aluminate phosphor, and a sulfide phosphor, has been proposed, as exemplified by a sialon phosphor, an oxynitride phosphor, or a nitride phosphor, which is characterized by low brightness deterioration caused by high energy excitation.
As one example of such an oxynitride phosphor, a phosphor in which an AlON crystal is activated by Mn is known (for example, refer to Patent Reference 1). This phosphor emits green light with high color purity having a peak from 510 to 520 nm and a narrow half width of the spectrum when it is excited by an ultraviolet ray, blue light, or an electron beam. Therefore, it is suitable as a green phosphor for the image display device.
Further, if Mg is added to the AlON crystal, it is reported that excitation characteristics by blue light of 440 nm to 460 nm may be improved (for example, refer to Patent Reference 2).
However, even though a phosphor in which the AlON crystal was activated by Mn exhibited high color purity of green, it could not be said that the excitation characteristics by blue light of 440 nm to 449 nm (also referred to as “blue light excitation characteristics”) were sufficient. Although the blue light excitation characteristics were improved when Mg was added to the AlON crystal, further improvement of the emission intensity was also in demand.